Method of generating alternating currents.



No." 821,838. PATENTED MAY -29, 1906.

W; STANLEY.

METHOD OF GENERATING ALTERNATING CURRENTS.

APPLICATION FILED JUNE 6, 1905.

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WILLIAM STANLEY, OF GREAT BARRINGTON, MASSACHUSETTS.

METHOD OF GENERATING ALTERNATING CURRENTSL Specification of Letters Patent.

Patented May 29, 1906.

Original application filed May 25, 1905, Serial No. 262,226. Divided and this application filed June 6, 1905. Serial No. 268,904.

ToaZZ whmn it may concern:

Be it known that 1, WILLIAM STANLEY, a citizen of the United States, residing at Great Barrington, county of Berkshire, Massachusetts, have invented certain new and useful Improvements in the Method of Generating Alternating Currents, 01 which the following is a full, clear, and exactdescription.

My invention relates to improvements in methods of generating alternating currents, and has for its object to provide for generating alternating currents of a desired potential gradient.

The purpose of my invention is to produce alternating currents which will have a substantially constant potential for all loads. This is brought about in the particular embodiment hereinafter described by the use of two generating elements which have opposite normal potential gradients when supplying unity power-factor currents. By normal potential gradient I mean the potential gradient which an element will have when energized by constant-potential currents. The potential gradients of these two elements can be combined soas to neutralize each other and produce a resultant potential gradient. The resultant potential gradient existing when the alternator is magnetized at constant potential I term the normal resultant potential gradient. The two elements descnbed each have a negative potential gradient when supplying lagging currents, pro ducing when combined a negative normal resultant potential gradient, so that by the use of an eXciter which has a complementary or positive potential gradient when the alternator is supplying lagging currents a constant potential can also be obtained from the alternator under these conditions.

The following is a description of an apparatus adapted to carry out my method, reference being had to the accompanying drawings, in which Figure 1 is an elevation of an alternator, partly in section. Fig. 1 is a partial lefthand side elevation of the apparatus of Fig.

- 1. Fig. 1 is a partial right-hand side elevation of said apparatus. of the stator-circuits. the rotor-circuits.

Referring more particularly to the drawings. AA are two stators. B B are two rotors mounted on a common shaft and having their windings connected to slip-rings O. D is an exciter supplying low-frequency alternating Fig. 2 is a diagram Fig. 3 is a diagram of windings b of the rotor B may be considered to form ten poles, while the winding 6 of the rotor B forms twelve poles. The windings on both rotor structures are multiphase and are supplied with alternating currents from the eXciter D, producing magnetic fields rotating relatively to the rotor or field structure at different polar speeds. The windings b and b are reversed relativelyto each other so that the fields produced by them rotate in opposite directions relatively to one another, as shown by the dotted arrows. (See Fig. 3.) Thus if the direction of rotation of the rotor is clockwise, as shown by the full arrows, (see Fig. 3,) the winding b,forming ten poles, will produce a field rotating magnetically clockwise or in the same direction relatively to the rotor, and the winding 1), forming twelve 'poles, will produce a field rotating counterclockwise or in the opposite direction relatively to the rotor. Such clockwise and counter-clockwise electromagnetic rotation of the fields combines with the structural rotation of the rotor to respectively increase (clockwise) and decrease (counter-clockwise) the effective rotation of the flux produced by the rotor, and consequently to increase and decrease the frequency of the electromotive forces and currents induced upon the stator circuit. Suppose that the eXciter D supplies currents of five periods and the rotors are revolving at the rate of siX hundred revolutions per minute. In that case with the construction above described the frequency of the currents from each stator would be fifty-five periods, for if the excitation were bycontinuous currents the periodicity of the current from the stator .A would be X 600 =50,

120 while the periodicity of the current from the rents are employed, the rotating fields of B produced by the exciting-currents travel faster than the rotor by five periods, and therefore increase the periodicity of the currents furnished by A, While the fields of B reduce by five per.ods the periodicity of the currents furnished by A, so that the periodicity of the current furnished by both A and A will be the same, or fiftyfive.

Now the element A B is operating below synchronism, and therefore its normal potential gradient is negative, while the element A B is operating above synchronism, and therefore its normal potential gradient is positive. If, therefore, the windings a (1/ of the two stator elements are connected in series, as shown in Fig. 2, the two gradients will neutralize one another to a greater or less extent, according to their several characteristics, and by proper proportionment can be made to neutralize each other entirely.

In case lagging. loads are supplied by the alternator the normal potential gradients of both elements Will be negative, producing a negative normal resultant potential gradient,

and under these conditions the exciter should have a positive potential gradient if the alternator isto supply constant-potential currentsthat is, the potential gradient of the exeiter should be complementary to the normal resultant potential gradient. By reason of the reaction of the alternator element under such conditions with proper proporti oning the exciter can be made to have such a positive potential gradient and to automatically neutralize the tendency of the alternator potential to fall under such conditions.

Energy-currents in the work-circuit tend to cause superimposed currents to How in the rotor-circuits which are opposite or substantially one hundred and eighty degrees apart. If, therefore, the rotors are so connected in parallel to the eXciter, as shown in Fig. 3, the exciter will be called upon to deliver to the machine magnetizing-currents only when the machine is delivering power factor unity load. hen the machines are delivering lagging currents, however, the superimposed rotor-currents are not one hundred and eighty degrees apart in phase or opposite to each other, but coincide in phase. Such superimposed currents will therefore flow through the exciting-circuit. Under these conditions, then, the characteristic of the alternator when excited by constant potential would be that of substantially constant potential when delivering power-factor unity load, the normal resultant potential gradient being zero and of decreasing potential when delivering power-factor zero load, the normal resultant potential gradient being negative. In order to maintain constant potential for any load, the exciter should therefore be constructed to give an increasing potential when the alternator is furnishing lagging currents and substantially constant potential when they are furnishing power-factor unity currents.

The windings shown in the diagram ar three-phase. The invention is obviously not limited to the use of such windings or to the particular relations or proportions mentioned, since it can also be carried out by other multiphase windings so long as the inducingfields rotate magnetically in different directions and the periodicities of the induced electromotive forces are the same.

This application is a division of the prior application filedby me on the 25th day of May, 1905, Serial No. 262,225, which application describes and claims the apparatus described herein.

What I claim is Q 1. The method of generating alternating currents of constant potential for variations of currents delivered which consists in generating two electromotive forces of equal frequency but opposite potential gradient, and neutralizing the variations of one such potential by the other.

2. The method of generating alternating currents 'which consists in producing two magnetic fields rotating magnetically inopposite directions, relatively to each other, inducing by such fields and the aid of mechanical motion electromotive forces of equal periodicities, combining said electromotive forces and producing alternating currents thereby.

The method of generating alternating currents which consists in producing by means of low-frequency alternating currents two electromagnetic fields rotating magnetically in opposite directions, inducing by such fields and the aid of mechanical motion electromotive forces of equal periodicities, combining said electromotive forces, producing \vorlvcurrents thereby and maintaining the potential gradient of the exciting-currents complementary to the normal resultant potential gradient of such Work-currents.

4. The method of generating alternating currents which consists in generatinglow-frequency currents, dividing said currents and producing by the divisions thereof two magnetic fields rotating magnetically in opposite directions relatively to each other, inducing by said fields and the aid of mechanical motion electromotive forces of equal periodicities, combining said electromotive forces and producing alternating currents thereby.

VVITJTJAM STANLEY. WVitnesses H. B. BRowNELL, L. VREELAND. 

